1. Field of the Invention
This invention relates to an automobile sensor for detecting the magnitude of a tensile force in a seat belt used in a car seat, and in particular to a sensor that can detect the magnitude of tension in a seat belt and provide an electrical signal that is representative of the magnitude of tensile force.
2. Description of the Related Art
Various devices are well known for their ability to measure force, pressure, acceleration, temperature, position, etc. by using a sensing structure combined with signal processing electronics. One general type of sensor or transducer for such applications is a resistive strain gauge sensor in which force or pressure is sensed or measured based on strain placed on the resistors. Resistive strain gauges function by exhibiting changes in resistance proportional to force which causes dimensional changes of the resistor.
Many types of strain gauge sensors have been designed and made commercially available. Various strain gauge sensors have proven to be generally satisfactory. Prior art sensors, however, have tended to be rather expensive and not suitable in certain applications such as sensing the presence of an occupant in an automobile seat. A sensor suitable for such an application must be compact, robust, impervious to shock and vibration and yet inexpensive.
Automobile seats can use sensors to activate air bags, which would be deployed during an accident. Injury to infants or small children from air bag deployment with excessive force is a current industry problem. A weight sensor in the seat can be used to control the deployment force during air bag activation.
Unfortunately there are several problems with detecting seat occupant weight. For example, when a seat occupant puts on a seat belt, the force of cinching down the seat belt on the occupant can cause a seat weight sensor to have false and erroneous readings. In another example, if a child""s car seat is cinched down tightly in the car seat, it can appear to the weight sensor that a heavy person is in the seat, which is the wrong reading.
A current unmet need exists for a reliable, low cost, simple and robust seat belt tension sensor that can be used to input additional seat occupant information to an airbag controller to control airbag deployment.
It is a feature of the invention to provide a reliable and cost-effective vehicle seat belt tension sensor for detecting the magnitude of tension in a seat belt when an occupant is in the seat.
An additional feature of the invention is to provide a seat belt tension sensor for attachment to a seat belt in a vehicle. The seat belt tension sensor includes a substrate having a top surface, a bottom surface and a pair of slots therethrough. The seat belt passes through the slots. The substrate has a pair of apertures. An actuator bar is located adjacent the top surface. The actuator bar has a first and second end. The ends pass through the apertures. The seat belt passes over the actuator bar. A load beam is attached to the substrate. The load beam has a first and second end. The ends of the actuator bar contact the ends of the load beam. At least one strain sensitive resistor is located on the load beam. The seat belt, when placed in tension, causes the actuator bar ends to flex the ends of the load beam placing stress on the strain sensitive resistor. The strain sensitive resistor generates an electrical signal in response to being placed under stress. The electrical signal changes as a function of tension on the seat belt.
The invention resides not in any one of these features per se, but rather in the particular combination of all of them herein disclosed and claimed and it is distinguished from the prior art in this particular combination of all of its structures for the functions specified. Other features of the present invention will become more clear from the following detailed description of the invention, taken in conjunction with the accompanying drawings and claims, or may be learned by the practice of the invention.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. Those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.